This invention relates to the field of multi-pole circuit breakers having a tripping mechanism of the toggle spring type.
Typically such mechanism include upper and lower toggle links pivotally connected on a toggle shaft with a spring connected between the toggle shaft and the cross arm of an operator. The operator is pivotally mounted to move the end of the spring connected thereto between a first position, in which the upper and lower links are flexed and the movable contact arm connected to the lower link is separated from the stationary contact, and a second position, in which the upper and lower links are extended and slightly over center with the movable contact arm connected to the lower link moved into contact with the stationary contact of the circuit breaker. The upper link is pivotally connected to a trip lever which is pivotally mounted to move between a latched position and an unlatched position. When in the latched position, the upper toggle link is pivotally anchored at its upper end on the trip lever to remain in the same location when the operator is moved to both its first and second positions, i.e. the contact separated position and contact closed position. The upper end of the upper toggle link remains anchored to the latched trip lever while the operator carries the spring and toggle shaft (which pivotally connects the upper toggle link at the other end to the lower toggle link) from the contact open position wherein the toggle links are flexed to the contact closed position carrying the toggle shaft to a slightly over center position wherein the toggle links become substantially extended to move the contact arm connected to the lower link into the contact closed position. When the trip lever is unlatched, the bias of the toggle springs on the toggle shaft is in a direction toward the end of the upper link which is connected to the trip lever, and laterally away from the latch member in a direction toward the operator cross arm to which the other end of the spring is connected, causes the trip lever to move away from the latch member and toward the cross arm of the operator which it contacts and which limits further movement of the trip lever. Such movement of the trip lever carriers the end of the upper toggle link anchored thereto forward beyond the pivot point of the toggle shaft to which the other end of the upper toggle link and one end of the lower toggle link are pivotally connected, enabling the bias of the spring on the toggle shaft to carry it toward the operator arm to which the other end of the spring is connected until the spring is substantially de-tensioned and the toggle mechanism collapsed with the toggle links flexed and the movable contact arm carried to the contact separated position.
In typical prior art circuit breakers of this type, the upper and lower toggle links are of electrically conductive metal, as is the movable contact blade connected to the lower toggle link. The toggle mechanism is thus electrically conductive in prior art circuit breakers and takes the polarity of the pole in which it is connected. The other poles of the circuit breaker must be insulated from the toggle mechanism or a phase to phase fault, or short circuit, would result. Such insulation is typically accomplished by a narrow toggle mechanism which can be centered over a single pole of the breaker, and then using a wide crossbar of phenolic or other insulating material in which to mount the movable contact blades of the other poles of the breaker.
Since the toggle shaft pivotally connecting the upper and lower toggle links of such prior art circuit breakers must be relatively short to center over only one pole of the breaker, there is space to connect only one spring in the usual breaker of this type between the toggle shaft and the crossarm of the operator. The single spring must be relatively long in order to provide the desired tripping energy to rapidly trip the breaker on occurrence of a fault current. Such circuit breakers therefore have a relatively high profile, or a depth of relatively large dimension.
It is desired to make circuit breakers of the type described above of lower profile, having a depth of smaller dimension. The present invention accomplishes such result by providing insulated lower links between the toggle shaft and contact blades whereby the toggle shaft is electrically neutral. It may, therefore extend across the entire width of a multi-pole circuit breaker and a plurality of relatively shorter toggle springs may be connected between the toggle shaft and the spaced apart crossarm of the operator. A plurality of the shorter toggle springs can be selected to equal the energy of a single longer toggle spring of a prior art breaker, and in this manner a lower profile breaker is achieved, having a depth of relatively smaller dimension.
Since each contact arm of the circuit breaker, in accordance with this invention, is connected to the toggle shaft through its own insulated lower link, it is possible for each contact blade to include the additional feature of being independently separable without separating the contacts of the other poles of the breaker. The independently separable contacts of the present invention include a movable contact mounted on a movable contact blade which is pivotally mounted to the insulated lower link of the toggle mechanism. The end of the contact blade opposite the contact end is biased by a cantilever spring in one direction which forces the contact end of the contact blade in the opposite direction to the contact closed position. Bias is applied to the contact blade in a manner such that each blade may independently blow apart as a result of electrodynamic and thermodynamic forces to a fully open position with no increase in bias force. This is not possible in prior art breakers in which individual contact blades are suspended from a common crossbar.